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In conventional ventilation large pressure changes (the difference between PEEP and PIP) create physiological tidal volumes and gas exchange is dependent on bulk convection (expired gas exchanged for inspired gas).
The large pressure changes and volumes associated with conventional ventilation have been implicated in the pathogenesis of ventilator induced lung injury (VILI) and chronic lung disease (CLD
On inspiration fast units receive most of ventilation , slow units still slowly, on expiration slow units may still be filling and actually inspires from exhaling fast units
this effect is accentuated @ higher frequencies with gas pendeling back and forth between adjacent units
taylor --Taylor dispersion is an effect in fluid mechanics in which a shear flow can increase the effective diffusivity of a species. Essentially, the shear acts to smear out the concentration distribution in the direction of the flow, enhancing the rate at which it spreads in that direction
Augmented diffusion that occurs because of turbulent flow between the axial and radial gas concentrations in the airways.
Asymmetrical Velocity Profiles
The high frequency bulk flow creates a “bullet” shaped flowprofile, with the central molecules moving further down the airway than those molecules found on the periphery of theairway.
The velocity profile is blunted so that at the completion of Each return, the central molecules remain further down the airway and the peripheral molecules move towards the mouth of the airway
DURING INPIRATION GASES AT CENTRE OF LUMEN HIGH PO2 LOW CO2 AND expiratory gases
Contrary to increasing freq in CMV on increasing freq in HFV there is not much change in CO2 Because it mainly depeds on TV2
Example comparing 6Hz and 8 Hz
1.assess the presence and symmetry of piston sounds.
Asymmetry may indicate improper ETT placement, pneumothorax, heterogeneous gross lung disease, or mucus plugging. Pause the piston to perform a cardiac exam and assess heart sounds.
With the piston paused you have placed the patient in a CPAP mode and will have maintained Paw.
2.Assess on CXR ETT placement Rib expansion (goal is 9 ribs) Pneumothorax / airleak syndrome Change in lung disease
3. Indications: Routine suctioning to ensure the ETT remains patent Frequency of suctioning varies by institution. Our policy is every 12 to 24 hours and prn. Decreased/absent wiggle Possibly from mucus plugs/secretions Decrease in SpO2 or transcutaneous O2 level Increase in transcutaneous CO2 level Suctioning de-recruits lung volume May be minimized but not fully eliminated with closed suction system. May require a sustained inflation recruitment maneuver following suctioning.
4 .COMPARISON OF MODES OF HFV
HIGH FREQUENCY VENTILATION - NEONATES
Dr. ADHI ARYA
SENIOR RESIDENT –GMCH -32 CHANDIGARH
• MECHANISM OF VENTILATION
• WHY HFV
• TYPES OF HFV
• TERMINOLOGY AND SETTINGS( INITIATION AND WEANING OFF)
• MONITORING/ROUTINE CARE ON HFV
HFV is a type of mechanical ventilation that uses a constant distending
pressure (mean airway pressure [MAP]) with pressure variations
oscillating around the MAP at very high rates
This creates small tidal volumes, often less than the dead space. HFOV
relies on alternative mechanisms of gas exchange such as molecular
diffusion, Taylor dispersion, turbulence, asymmetric velocity profiles,
Pendelluft, cardiogenic mixing and collateral ventilation
NATURAL HIGH FREQUENCY VENTILATION
• DOG’S PANTING
MECHANISM OF ACTION
•ALVEOLAR VENTILATION = (Vt-Vd) * RATE
• IN HFV Vt< Vd, so actualluy no ventilation
HFV Provides augmented gas distribution by means of numerous
gas transport mechanisms.
Convection ventilation( bulk flow)
Asymmetric velocity profiles
Convection, Transit Time and Direct
is the transport of air flow at a
constant equal velocity that is
parabolic in shape.
TO SHORT PATH LENGTH UNITS
THAT BRANCH OFF FROM
At the end of expiration:
• Alveoli with short time constants (fast alveoli
units) are empty.
• Alveoli with longer time constants (slow alveoli
units) are still emptying
• Gases will move from slow units to fast units
because of pressure gradients between the
The relationship between:
Axial velocity profile (Turbulence)
the diffusion of gases in motion
and the branching network of the lungs.
Airflow moving through the airways moves in a u-shape formation. At the center of the lumen air
will move at a faster velocity, than air that is closest to the wall.
Occurs with rapid respiratory cycles. Gases (O2) at the center of the lumen will advance further into
the lungs as gases (CO2) along the wall of the airway moves out towards the mouth.
• Asymmetrical Velocity Profiles
• The high frequency bulk flow creates a “bullet” shaped flow profile, with the central molecules
moving further down the airway than those molecules found on the periphery of the airway.
• The velocity profile is blunted so that at the completion of each return, the central molecules
remain further down the airway and the peripheral molecules move towards the mouth of the
As the heart beats the heart provides additional peripheral mixing
by exerting pressure against the lungs during contraction of the
This pressure promotes the movement of gas flow through the
neighboring parenchymal regions.
Collateral VentilationMolecular Diffusion
Maintaining a constant distending
pressure with HFV within the
lungs along with movement of gas
molecules promotes gas diffusion
across the alveolar membrane, at
a faster rate.
Collateral ventilation increases
with HFV due to connections
between the alveoli
(Pores of Kohn)
• SMALL TIDAL VOLUMES
limits alveolar over distension
• HIGHER MAP
Better alveolar recruitment
• CONSTANT mPaw during inp and exp
preventing end alveolar collapse
Zone of Overdistention
Goal is to avoid injury zones
and operate in the safe window
HFOV is used to prevent Ventilator Induced Lung Injury
Pressure and Volume Swings
During CMV, there are swings between the zones of
injury from inspiration to expiration.
During HFOV, the entire cycle operates in the “safe
window” and avoids the injury zones.
TYPES OF HFV
Based on characteristic of exhalation (Active /Passive/ Hybrid )and
source of generation
– 3 types
1. failure of conventional ventilation in the term infant (Persistent
Pulmonary Hypertension of the Newborn [PPHN], Meconium
Aspiration Syndrome [MAS]).4,5
2. Air leak syndromes (pneumothorax, pulmonary interstitial
3. Failure of conventional ventilation in the preterm infant (severe
RDS, PIE, pulmonary hypoplasia) or to reduce barotrauma when
conventional ventilator settings are high.
4. Lung hypoplasia syndromes
• SEVERE RESPIRATORY FAILURE
One-study sites that 50% of infants studied who met the criteria for
ECMO were successfully managed with HFV alone.
• Initially, start with a MAP 2 cm higher than with conventional
ventilation and incrementally increase it. Very high MAPs may be
needed to achieve adequate oxygenation.
• PERSISTENT PULMONARY HYPERTENSION
• Hyperventilate to achieve a PaCO2 of 25-35 Torr with a pH of 7.45-7.55. Some
literature suggests a pH of 7.55-7.65.
• Hyperoxygenate generally by maintaining the FIO2 at 1.0. Increase the MAP to
maintain adequate oxygenation
LUNG HYPOPLASIA SYNDROMES
• Initially use the same MAP as on conventional ventilation then
aggressively increase in 1cm increments to optimum lung volume.
• Adjust the amplitude to give a PaCO2 of 45-50.
• AIR LEAK SYNDROMES
• • Initially set the MAP 1-2 cm H2O below the MAP on conventional
3. CXR (1hr after initiation or any change in settings/deterioration)
5. BP MONITORONG
lung recruitment maneuver.
• There are several ways in which to perform a SI maneuver.
• In our institution, the piston is paused (thus leaving the patient in CPAP) and the Paw
is increased by 8-10 cm H2O for 30-60 seconds.
• Once the SI maneuver is completed, the piston is restarted.
• Potential complications:
• CV compromise / altered hemodynamics
When To Utilize A SI Maneuver
• When initiating HFOV to recruit lung
• After a disconnect or loss of FRC/Paw
• After suctioning (even with a closed suction system)
• Inability to wean FiO2
• When considering increasing Paw
• A recruitment maneuver may recruit lung allowing you to
maintain the baseline Paw and, thus, not increase support.
EVIDENCE ( should answer these three
PULMONARY OUTCOMES OF CONTROLLED TRIALS OF HFV
DURING SURFACTANT ERA AND SYNCHRONOSED VENTILATION
AS PRIMARY MODE
• AS A PRIMARY MODE
Elective high frequency ventilation compared to conventional
mechanical ventilation in the early stabilization of infants with
respiratory distress - Cochrane-March 2015
Insufficient evidence exists to support the routine use of high
frequency oscillatory ventilation instead of conventional ventilation for
AS RESCUE THERAPY
Rescue high-frequency jet ventilation versus conventional ventilation
for severe pulmonary dysfunction in preterm infants
Cochrane oct 2015
• Existing evidence does not support the use of rescue high-frequency
jet ventilation compared with conventional mechanical ventilation for
treatment of preterm infants with severe pulmonary problems
AS RESCUE THERAPY
• High frequency oscillatory ventilation versus conventional
ventilation for infants with severe pulmonary dysfunction born at or
cochrane may 2009
There are no data from randomized controlled trials supporting the use
of rescue HFOV in term or near term infants with severe pulmonary
HFJV VS HFOV
• High frequency jet ventilation versus high frequency oscillatory
ventilation for pulmonary dysfunction in preterm infants
Cochrane database May 2016
• no evidence to support the superiority of HFJV or HFOV as elective or